Image displaying device

ABSTRACT

A main object of the present invention is to make it possible to supply current to electric field light emitting elements without decreasing the aperture ratio of pixels. In order to achieve the object, the present invention provides an image displaying device wherein: current driven typed light emitting elements and transistors for current driving are formed on a same substrate; comprising a plurality of display cells having such a structure that the current driven typed light emitting elements and transistors for current driving are connected in between a power supply line and a ground line; the transistors for current driving are selectively driven to conduct display; and a power supply electrode column for supplying currents to each display cell is formed on a power supply common electrode that is formed on a surface of a facing substrate parallel to the substrate.

TECHNICAL FIELD

The present invention relates to an image displaying device usingcurrent driven typed light emitting elements such as organic lightemitting elements.

BACKGROUND ART

FIG. 4 is a diagram showing an example of an image displaying deviceusing organic light emitting elements. FIG. 4A is a sectional view, andFIG. 4B is a top view.

Insulating layers 2 and 3 are laminated on a glass substrate 1, and ananode 4 made of a transparent conductive film which prescribes eachlight emitting area, is formed thereon. And further, on the entiresurface thereof, an organic light emitting layer 5 and a cathode 6 areformed. Moreover on the glass substrate 1, a transistor for currentdriving 8 which current is supplied via a power supply line 7, atransistor 9 for ON/OFF control of the transistor for current driving 8,and a vertical electrode 10 and a horizontal electrode 11, for selectingdisplay cells to emit light, are formed. The vertical electrode 10 andthe horizontal electrode 11 are insulated by the insulating layer 2.Each transistor is protected by the insulating layer 3, and also asurface on the transistor is smoothed. In addition, the transistor forcurrent driving 8 is connected to the anode 4 via a through hole of theinsulating layer 3. Moreover, a facing seal plate 12 is provided so asto cover the entire cathode 6 for hermetically sealing the imagedisplaying device.

In the image displaying device having such a configuration, when thetransistor 9, of a display cell selected by the vertical electrode 10and the horizontal electrode 11, turns on, the transistor for currentdriving 8 turns on, and a current flows from the power supply line 7through the anode 4, the organic light emitting layer 5 and the cathode6, thus the selected cell emits light. This light emitting state iscontinued until a signal for turning off is applied to the transistor 9.By thus selecting and driving each light emitting cell arranged in amatrix form by transistors, image display is conducted.

The current driven typed light emitting element such as the organiclight emitting element emits light by applying current through it, sothat, for maintaining the light emitting state, it is necessary tocontinue applying the current flow. Therefore, for active matrix drivingof a current driven typed light emitting element, at least two activeelements are needed, one is an element to keep applying the current flowand another is an element to control the former element. Furthermore, tokeep applying the current flow, a dedicated current supply line isneeded.

As shown in FIG. 4, the current driven typed light emitting element isconnected to the transistor for current driving 8, and connected inbetween the common power supply line 7 and a common installed line(cathode). At least two transistors are required for one current driventyped light emitting element. As for the wiring, four electrodes of adata line for selecting a current driven typed light emitting element, ascanning line (the vertical electrode and the horizontal electrode), thepower supply line, and a ground line are needed, resulting in acomplicated structure. Especially, as the number of display pixelsincreases, the power supply line is required to have low resistancebecause higher current supply capability is required. There is a problemthat the aperture ratio of pixels is decreased if the line width isincreased in order to lower the resistance.

Furthermore, since the yield of the transistor circuit part and thecurrent driven typed light emitting elements are different, there isalso a problem that it is difficult to ensure a high yield and a highquality as the whole.

In some cases, a color conversion method is used in the current driventyped light emitting elements. In the color conversion method, light ofa light emitting layer of a specific color is converted to light ofanother color by using a fluorescent dye. For example, apart of light ofthe blue color light emitting later is converted to green or red. Inthis case, the color conversion layer is formed so as to be connected tothe light emitting layer. For active matrix driving of organic lightemitting elements of such a color conversion method, the following twomethods are conceivable.

(1) Thin film transistors are formed on a color conversion layer, andfurther, an organic electric field light emission layer is formedthereon.

(2) An organic electric field light emission layer is formed on thinfilm transistors, and further, a color conversion layer is formedthereon.

In the method of (1), the color conversion layer is formed, andthereafter the transistors are formed thereon. Therefore, the colorconversion layer is required to have heat resistance of at least theprocess temperature 400° C. at the time of transistor fabrication, andit is extremely difficult. On the other hand, in the method of (2), thecolor conversion layer is formed on the light emitting layer. However,since the light emitting layer is extremely vulnerable to moisture, itis extremely difficult to form the color conversion layer directly onthe light emitting layer.

As a countermeasure against them, application of, not the bottomemission method in which light is taken out from the glass substrateside as shown in FIG. 4, but the top emission method in which light istaken out from the cathode side is conceivable. This aims to implementactive matrix driving of the color conversion method by individuallyfabricating a substrate having a light emitting layer using atransparent cathode formed thereon and a substrate having a colorconversion layer formed thereon, and then putting the substratestogether. In addition to a problem in reliability of the transparentcathode, there is a problem that the image quality is degraded becausethe light emitting layer and the color conversion layer are opticallyseparated so that the occurrence of optical crosstalk is inevitable.

DISCLOSURE OF THE INVENTION

The present invention aims to solve the above mentioned problems. Anobject of the present invention is to make it possible to supply acurrent to light emitting elements without decreasing the aperture ratioof pixels and maintain light emitting elements having high quality witha high yield.

Moreover, in the case where the color conversion method is used forcurrent driven typed light emitting elements, an object is to make itpossible to conduct active matrix driving of the current driven typedlight emitting elements without optical crosstalk and without using atransparent cathode.

Therefore, the present invention provides an image displaying devicewherein: current driven typed light emitting elements and transistorsfor current driving are formed on a same substrate; comprising aplurality of display cells having such a structure that the currentdriven typed light emitting elements and transistors for current drivingare connected in between a power supply line and a ground line; thetransistors for current driving are selectively driven to conductdisplay; and a power supply electrode column for supplying currents toeach display cell is formed on a power supply common electrode that isformed on a surface of a facing substrate parallel to the substrate.

Moreover, in the above mentioned invention, it is preferable that thepower supply electrode column is connected to a power supply padprovided at a notch that is formed in a part of a cathode formed on thecurrent driven typed light emitting element, and is connected to thetransistor for current driving via the pad.

Further, the present invention provides an image displaying device,wherein a substrate having transistors for current driving formedthereon and a substrate having current driven typed light emittingelements formed thereon are faced to each other, and an image isdisplayed by driving the transistors for current driving and supplyingcurrents individually to each pixel of the current driven typed lightemitting elements through a power supply electrode column extendingbetween both substrates.

In the above mentioned invention, it is preferable that an anode, alight emitting layer, and a cathode are formed, in this order, on thesubstrate having current driven typed light emitting elements formedthereon; also a notch is formed in the light emitting layer and in thecathode per every anode; and the power supply electrode column,extending from the substrate having the transistors for current drivingformed thereon, is connected to the notch.

In the present invention, the current driven typed light emittingelements may have a color conversion layer.

In the above mentioned invention, it is preferable that a colorconversion layer, an anode, a light emitting layer, and a cathode areformed, in this order, on the substrate having current driven typedlight emitting elements formed thereon; also a notch is formed in thelight emitting layer and in the cathode per every anode; and the powersupply electrode column, extending from the substrate having transistorsfor current driving formed thereon, is connected to the notch.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of an image displaying device ofthe present invention;

FIG. 2 is a diagram showing another example of an image displayingdevice of the present invention;

FIG. 3 is a diagram showing another example of an image displayingdevice of the present invention; and

FIG. 4 is a diagram showing a conventional example of an imagedisplaying device using organic light emitting elements.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention relates to an image displaying device usingcurrent driven typed light emitting elements, such as organic lightemitting elements. This image displaying device is characterized in thata power supply electrode column for supplying a current is providedbetween a substrate having current driven typed light emitting elementsformed thereon and another substrate facing across the current driventyped light emitting elements. In the present invention, it is possibleto realize an image displaying device in which a current can be suppliedto electric field light emitting elements without decreasing theaperture ratio of the pixel part by providing the above mentioned powersupply electrode column.

There are three embodiments in the image displaying device of thepresent invention. In a first embodiment, a power supply commonelectrode is provided on a substrate facing a substrate having currentdriven typed light emitting elements formed thereon, and a current issupplied from the power supply common electrode via a power supplyelectrode column formed in between the substrates. In a secondembodiment, transistors for current driving and an organic lightemitting layer are respectively formed on different substrates, andthose substrates are connected by a power supply electrode column tosupply a current. In a third embodiment, transistors for current drivingand an organic light emitting layer having a color conversion layer areformed on different substrates, and those substrates are connected by apower supply electrode column to supply a current.

Hereafter, an image displaying device of each embodiment of the presentinvention will be described.

1. FIRST EMBODIMENT

First, a first embodiment in an image displaying device of the presentinvention will now be described. An image displaying device of thepresent embodiment will be described with reference to FIG. 1. FIG. 1 isa diagram showing an example of an image displaying device of thepresent embodiment. FIG. 1A is a sectional view, and FIG. 1B is a topview. The same numerals as those shown in FIG. 4 denote the samecontents, so that detailed description thereof will be omitted.

In the present embodiment, insulating layers 2 and 3, an anode 4 formedof a transparent conductive film, an organic light emitting layer 5, anda cathode 6 are formed on a glass substrate 1. In addition, a current issupplied to the anode 4 via a transistor for current driving 8 formed onthe glass substrate 1.

In the present embodiment, a power supply common electrode 20 is formedon an entire surface of a facing substrate 13 (corresponding to thefacing seal plate 12 in FIG. 4), which is located so as to be faced tothe glass substrate 1, facing to the cathode 6. A power supply electrodecolumn 21, for supplying a current to the transistors for currentdriving 8 of each display cell, is formed on the power supply commonelectrode 20. The power supply electrode column is formed of metal orconductive resin. The power supply electrode column also has a functionas a spacer between substrates. In a part of the cathode 6 and theorganic light emitting layer 5 which are formed on the entire surface ofthe glass substrate 1, a notch is formed per every anode prescribingeach light emitting area of display cells. In this part, a power supplypad 22 is formed, and is connected to each power supply electrode column21.

In such a configuration, a voltage from the power supply commonelectrode 20 on the facing substrate is always applied to thetransistors for current driving 8 through the power supply electrodecolumn 21 and the power supply pad 22. Therefore, if the transistor 9 inthe display cell selected by the vertical electrode 10 and thehorizontal electrode 11 turns on, then the corresponding transistor forcurrent driving 8 turns on, and a current flows through the anode 4, theorganic light emitting layer 5 and the cathode 6 so that the selectedcell emits light.

In this way, the power supply lines are not formed on the glasssubstrate 1 and a current is supplied from the power supply electrodecolumn 21, which extends from the facing substrate perpendicularly,unlike the conventional technique. Therefore, the light emitting area isnot restricted by the power supply line, and a high aperture ratio canbe ensured. As for the facing substrate 12, it is provided as the sealplate in the conventional technique as well, and the seal plate is alsoused to form the power supply common electrode. Therefore, whilemaintaining the conventional structure, the aperture ratio can beincreased.

In the conventional technique, when conducting active matrix driving ofcurrent driven typed light emitting elements, such as organic lightemitting elements, wiring for supplying power to each pixel is needed onthe same plane as the light emitting elements, being a factor ofdecreasing the aperture ratio of the pixels. In the present embodiment,however, the power supply common electrode is formed on the facing sealsubstrate, and a current is supplied from the power supply commonelectrode to each pixel through the power supply electrode column.Therefore, the power supply lines on the substrate of the light emittingelement side are no longer necessary, and it becomes possible to realizea high aperture ratio.

2. SECOND EMBODIMENT

A second embodiment in an image displaying device of the presentinvention will now be described. The image displaying device of thepresent embodiment will be described with reference to FIG. 2. In thepresent embodiment, a substrate having transistors for current drivingformed thereon and a substrate having an organic light emitting layerformed thereon are separated. And facing both substrates to each other,a current is supplied per every display cell through a power supplyelectrode column that extends in between the substrates. A current issupplied without decreasing the aperture ratio, and both substrateswhich differ in yield can be produces separately.

A transistor for current driving 8, a transistor for ON/OFF control ofthe transistor for current driving 8, and a vertical electrode and ahorizontal electrode for selecting a display cell that should emit lightare formed on a glass substrate 1. From a power supply pad 22 which isconnected to the transistor for current driving 8, a power supplyelectrode column 21 penetrates to the surface through an insulatinglayer 3 and extends to the facing substrate. The vertical electrode andthe horizontal electrode are insulated by an insulating layer 2. Eachtransistor is protected by the insulating layer 3, and the surfaces onthe transistors are smoothed. Since electrodes are not formed on theinsulating layer 3 in the present embodiment, it is also possible toomit this.

On the other hand, on a glass substrate 13 facing to the glass substrate1, an anode 23 formed of a transparent electrode is formed per eachdivision, which prescribe light emitting areas. An organic lightemitting layer 24 and a cathode 25 are laminated on the anode over theentire surface of the substrate. A notch is formed in a part of theorganic light emitting layer 24 and the cathode 25 per every anodes andthe power supply electrode column 21 is connected to the anode 23through this part. The power supply electrode column 21 is formed ofmetal or conductive resin, and also has a function as a spacer betweenthe both substrates.

In such a configuration, when a transistor, selected by the verticalelectrode and the horizontal electrode formed on the glass substrate 1side, turns on, the pertinent transistor for current driving 8 turns on,and a current flows through the power supply electrode column 21 whichis connected to the transistor for current driving 8, the anode 23 whichis formed of the corresponding transparent conductive film, the organiclight emitting layer 24 and the cathode 25 to make the selected cellemit light. An optical output is obtained from the glass substrate 13side through the transparent conductive film.

In this way, in the present embodiment, the glass substrate 1 side isused as the circuit substrate for selecting and driving the currentdriven typed light emitting elements, and the current driven typed lightemitting elements are formed on the side of the glass substrate 13,which is facing to the glass substrate 1. Current supply to the currentdriven typed light emitting elements is conducted by the power supplyelectrode column 21 which extends vertically from the glass substrate 1side. Therefore on the substrate of the current driven typed lightemitting elements side, the transistors for current driving and wiringfor them are no longer necessary so that the light emitting area is notrestricted by the power supply line and the like, and a high apertureratio can be ensured. In addition, quality control of the substrate forthe transistor circuit for current driving and the quality control ofthe substrate for the current driven typed light emitting elements canbe done separately.

In the conventional technique, when conducting active matrix driving ofcurrent driven typed light emitting elements such as organic lightemitting elements, wiring for supplying power to each pixel is needed onthe same plane as the current driven typed light emitting elements,resulting to be a factor of decreasing the aperture ratio of the pixels.In the present embodiment, however, the substrate for transistor circuitfor current driving and the substrate for the current driven typed lightemitting elements are separated, faced to each other, and a current issupplied from the facing substrate for the transistor circuit forcurrent driving to each pixel. Therefore, the transistors for currentdriving and wiring for them on the substrate for the current driventyped light emitting elements are no longer necessary, and it becomespossible to realize a high aperture ratio.

In addition, the substrate which forms the current driven typed lightemitting elements can be completely separated from the substrate whichforms the driven elements. Therefore, individual quality control becomespossible, and an extremely high quality can be ensured.

3. THIRD EMBODIMENT

A third embodiment in an image displaying device of the presentinvention will now be described. The image displaying device of thepresent embodiment will now be described with reference to FIG. 3. Inthe present embodiment, a substrate having transistors for currentdriving formed thereon and a substrate having an organic light emittinglayer with a color conversion layer formed thereon are separated, facedto each other, and a current is supplied per every display cell throughan electrode column that extends between the both substrates.

A transistor for current driving 8, a transistor for ON/OFF control ofthe transistor for current driving 8, and a vertical electrode and ahorizontal electrode, for selecting a display cell that should emitlight, are formed on a glass substrate 1. From a power supply pad 22which is connected to the transistor for current driving 8, a powersupply electrode column 21 penetrates to the surface through aninsulating layer 3 and extends to the facing substrate. The verticalelectrode and the horizontal electrode are insulated by an insulatinglayer 2. Each transistor is protected by the insulating layer 3, and thesurfaces on the transistors are smoothed. Since electrodes are notformed on the insulating layer 3 in the present embodiment, it is alsopossible to omit this.

On the other hand, on a glass substrate 13 facing to the glass substrate1, a color conversion layer 26 is formed by patterning in aphotolithography process. On the color conversion layer 26, an anode 23formed of a transparent electrode is formed per each division, whichprescribes each light emitting area. An organic light emitting layer 24and a cathode 25 are laminated on the anode over the entire surface ofthe substrate. A notch is formed in a part of the organic light emittinglayer 24 and the cathode 25 per every anode, and the power supplyelectrode column 21 is connected to the anode 23 through this part. Thepower supply electrode column 21 is formed of metal or conductive resin,and also has a function as a spacer between the both substrates.

In such a configuration, a transistor for current driving 8, selected bythe vertical electrode and the horizontal electrode formed on the glasssubstrate 1 side turns on, and a current flows through the power supplyelectrode column 21 which is connected to the transistor for currentdriving, the anode 22 formed of the corresponding transparent conductivefilm, the organic light emitting layer 23 and the cathode 24 to make theselected cell emit light. Apart of light that has passed through thetransparent conductive film is converted by the color conversion layer26. A color optical output is obtained from the side if the glasssubstrate 13.

In this way, in the present embodiment, the glass substrate 1 side isused as the circuit substrate for selecting and driving the currentdriven typed light emitting elements, and the current driven typed lightemitting elements with color conversion layer are formed on the glasssubstrate 13, which is faced to the glass substrate 1. Therefore, it ispossible to form current driven typed light emitting elements with thecolor conversion layer with extreme ease and conduct highly definiteimage display. In addition, quality control of the transistor circuitsubstrate for current driving and the quality control of the substratefor the current driven typed light emitting elements can be doneseparately.

In the conventional technique, when conducting active matrix driving ofcurrent driven typed light emitting elements such as organic lightemitting elements, by using the color conversion method, it isinevitable to use an extremely complicated layer configuration, or use atransparent cathode with the top emission structure, and occurrence ofoptical crosstalk is inevitable. According to the present embodiment, itis possible to obtain a highly definite image displaying device, conductindividual quality control of the both substrates, and ensure anextremely high quality, by forming the substrate having the transistorsfor current driving formed thereon and the current driven typed lightemitting elements with the color conversion layer formed thereon.

The present invention is not restricted by the above mentionedembodiments. The above mentioned embodiments are nothing but examples.Whatever having substantially the same configuration and bringing aboutthe same operation effects as the technical thought described in claimsof the present invention is incorporated in the technical range of thepresent invention.

1-2. (canceled)
 3. An image displaying device, wherein a substratehaving transistors for current driving formed thereon and a substratehaving current driven typed light emitting elements formed thereon arefaced to each other, and an image is displayed by driving thetransistors for current driving and supplying currents individually toeach pixel of the current driven typed light emitting elements through apower supply electrode column extending between both substrates.
 4. Theimage displaying device according to claim 3: wherein an anode; a lightemitting layer, a cathode are formed, in this order, on the substratehaving current driven typed light emitting elements formed thereon; alsoa notch is formed in the light emitting layer and in the cathode perevery anode; and the power supply electrode column, extending from thesubstrate having the transistors for current driving formed thereon, isconnected to the notch.
 5. The image displaying device according toclaim 3, wherein the current driven typed light emitting elements areprovided with a color conversion layer.
 6. The image displaying deviceaccording to claim 5: wherein a color conversion layer, an anode, alight emitting layer, and a cathode are formed, in this order, on thesubstrate having current driven typed light emitting elements formedthereon; also a notch is formed in the light emitting layer and in thecathode per every anode; and the power supply electrode column,extending from the substrate having transistors for current drivingformed thereon, is connected to the notch.